The Siberian Traps - Area and Volume

The Siberian Traps (basalts, tuffs and near-surface intrusive rocks) cover approximately 2.5 x 106 km2, or 60%, of the Siberian craton (Fedorenko et al., 1996). The area of basalts beneath the West Siberian Basin is not well constrained, but is estimated at between 0.75 x 106 km2 (Zhuravlev, 1985) and 'at least' 1.3 x 106 km2 (Reichow et al., 2002). Basalts are also found on the Taimyr Peninsula and, if these basalts are related to those on the Siberian craton, it is very likely that more material is buried beneath the intervening Yenesei-Khatanga Trough. The Traps may also extend beneath the Kara Sea (Vyssotski et al., 2005).

Estimating the original extent of the Traps is difficult, given the likely erosion over the last 250 Ma. This is especially important for the relatively easily eroded pyroclastic deposits. Whilst preservation may have been improved by burial in the West Siberian Basin and Yenesei-Khatanga Trough, it is unclear how much tectonic uplift and erosion occurred in these basins during the early Triassic, prior to burial. Milanovskiy (1976) estimated that the original extent of the Traps was about 4 x106 km2, but there must be considerable latitude in this figure. Masaitis (1983), for example, has suggested that the Traps originally extended over a region of ~7 million km2.

Note that these figures refer to the present day, and take no account of erosion since emplacement.

Uncertainties grow when calculating the present-day or original volumes of magmatic products. The thickest part of the lava sequence are found in Noril'sk (maximum thickness ~3500 m: Wooden et al., 1993), thinning south-eastwards across the Siberian craton into Putorana (~1800 m: Sharma et al., 1991, 1992, 1997) and Nizhnyaya-Tunguska (~ 1000 m: Zolutukhin and Al'Mukamedhov, 1991) . In Maymecha-Kotuy, the sequences are in excess of 3000 m (Fedorenko et al., 1996). Intrusives and tuffs are important components on the Siberian craton, with average thicknesses of 250 m and 350 m, respectively (Fedorenko et al., 1996). Thickness in the West Siberian Basin, Yenesei-Khatanga Trough and Kara Sea are largely unknown. Basalt sequences thicken to over 4000 m northwards from Noril'sk into the Yenesei-Khatanga Trough (Fedorenko et al., 1996). Deep borehole SG-6 in the Urengoy rift drilled over 1 km of basalt before terminating, and it is estimated from seismic data that there is at least a further 1 km of basalt below this (Westphal et al., 1998).

Milanovskiy (1976) concluded that the original volume of the Traps and related rocks exceeded 2 x106 km3, and Masaitis (1983) estimated their volume to be ~ 4 x 106 km3. Reichow et al. (2002) estimated the present-day volumes to be around 2.3 x 106 km3, but their estimate did not take into account any igneous rocks in the Yenesei-Khatanga Trough, Taimyr Peninsula, or beneath the Kara Sea. Any 'working estimate' for the total volume of erupted magmatic products is likely to be at least 3 x106 km3, and possibly as much as 5 x106 km3.

None of these estimates considers the volume of deeply-seated intrusions (e.g. magmatic underplate at the base of the crust, and frozen magma bodies in the lower and middle crust). If the Siberian Traps are analogous to the North Atlantic Igneous Province, it is likely that many million cubic kilometers of material lie buried at depth in the crust or uppermost mantle.